This invention relates to an ultrasonic method for quality testing of packaged products.
The degradation of foods contained in bags and pouches can be easily ascertained, for example by the visual inspection of the packages for signs of expansion when the contents liberate gases on putrefaction or degradation and, hence, cause expansion of the containing bags or by the visual inspection of the contents through the bags, provided that the bags are of the see-through type, when the contents putrefy or degrade without evolution of gases. If the bags cannot be seen through, an appropriate number of samples are taken at random, the bags are broken and the contents are visually inspected.
However, the visual inspection for the expansion of bags is valid only when the putrefaction has progressed to a marked extent and cannot be a useful method at an early or intermediate stage of putrefaction where the evolution of gases is not large enough, for the lack of expansion of a bag does not necessarily mean that the contents have not undergone degradation or putrefaction.
The visual inspection through light-transparent bags is not successful, either, at a stage where spoilage has not progressed far enough. Thus, it is inevitable to destroy the bags for confirmation.
Recent foods are often available as packaged in aluminum foil-laminated plastic film and, in such cases, the above destructive inspection method is the only method available.
However, the method comprising sampling out a large number of packages and testing them is very disadvantageous in terms of procedural complexity. Moreover, since even acceptable products are made unacceptable by unpackaging, this method has the drawback of increased unit production cost. For a complete quality check, the sample size must be sufficiently large but since it is impossible to unpackage so many products, the method is inadequate in reliability.
Further, irrespective of whether the bags are transparent and the contents are visible from outside or the bags are made of opaque material and broken for inspection of the contents, the visual examination is not necessarily a reliable method of inspection. Moreover, the examination accuracy is dependent on individual inspectors.
It is, therefore, an object of this invention to provide a non-destructive method for accurate evaluation of packaged products for spoilage and other quality parameters.
It is another object of this invention to provide an apparatus which can be advantageously employed for the purpose of practicing the above-mentioned non-destructive method.